AUKE BAY LABORATORY (ABL) (cont.)

Steller Sea Lion Prey Study

As part of ongoing research to assess Steller sea lion (Eumetopias jubatus) prey, hydroacoustic cruises were conducted in Lynn Canal and Frederick Sound, Alaska, during September 2003 aboard the chartered fishing vessel Viking Storm. Hydroacoustic (echosounding) transects in open water and bays were coupled with trawl catches to verify hydroacoustic assessment of fish species.

The majority of the 3,122 kg of fish caught were juvenile walleye pollock (Theragra chalcogramma), followed by Pacific hake (Merluccius productus), jellyfish, mature walleye pollock, northern lampfish (Stenobrachius leucopsarus), rockfish (Sebastes spp.), and eulachon (Thaleichthys pacificus) (Fig. 2). Relative to previous cruises, jellyfish and squid were more abundant. Mature pollock were less abundant than previously observed and were seemingly replaced by hake, particularly in the open water. Species never before encountered in the hydroacoustic cruises were caught in both study areas, including a relatively large species of myctophid in Lynn Canal preliminarily identified as pinpoint lampfish (Nannobrachium regale). In Frederick Sound, newly encountered species included big skates (Raja binoculata), longnose skates (R. rhina), spotted ratfish (Hydrolagus colliei), Pacific halibut (Hippoglossus stenolepis), sablefish (Anoplopomus fimbria), an Okhotsk snailfish (Liparus ochotensis; preliminary identification), and redbanded rockfish (Sebastes babcocki).

A total of 229 walleye pollock, Pacific herring (Clupea pallasi), eulachon, capelin (Mallotus villosus), and Pacific hake were collected for nutritional analysis with particular emphasis on demersal samples. Samples of Steller sea lion scat were collected from each of the three haulouts visited (Sunset Island, Brothers Island, and Sail Island). Of the branded animals observed during the scat collections, 18 were photographed. Independent analysis of the photographed brands will be combined with the field observations to improve brand accuracy.

In addition to the hydroacoustic survey, the first longline cruise to examine benthic prey species was completed in Frederick Sound during September 2003 aboard the chartered fishing vessel Antares. Nearly half of the 6,000 kg of catch was Pacific halibut, followed by sablefish, Pacific cod (Gadus macrocephalus), arrowtooth flounder (Atheresthes stomias), skates, and rockfish (Fig. 3 above). Species caught in quantities less than 1% of the catch by mass included Pacific sleeper sharks (Somniosus pacificus), walleye pollock, Dover sole (Microstomus pacificus), spiny dogfish (Squalus acanthius), and spotted ratfish.

By Johanna Vollenweider and Mike Sigler.


2003 Sablefish Longline Survey Completed

The Alaska Fisheries Science Center (AFSC) has conducted an annual longline survey of sablefish and other groundfish in Alaska from 1987 to 2003. The survey is a joint effort involving two AFSC research divisions: the Auke Bay Laboratory and Resource Assessment and Conservation Engineering Division. The survey replicates as closely as practical the Japan-U.S. cooperative longline survey conducted from 1978 to 1994 and also samples gullies not sampled during the cooperative longline survey. In 2003, the twenty-fifth annual longline survey of the upper continental slope of the Gulf of Alaska and the eastern Bering Sea was conducted. One hundred fifty-two longline hauls (sets) were completed between 1 June and 1 September 2003 by the chartered fishing vessel Ocean Prowler. Sixteen kilometers of groundline were set each day, containing 7,200 hooks baited with squid.

Sablefish was the most frequently caught species, followed by giant grenadier (Albatrossia pectoralis), Pacific cod, and shortspine thornyhead (Sebastolobus alascanus). A total of 87,141 sablefish were caught during the survey; 4,055 sablefish, 535 shortspine thornyhead, and 100 Greenland turbot (Reinhardtius hippoglossoides) were tagged and released during the survey. Electronic temperature-depth tags were surgically implanted in 45 Greenland turbot and 55 shortspine thornyheads. This is the first time these species have been tagged with electronic tags. Length-weight data and otoliths were collected from approximately 2,300 sablefish. Killer whales (Orcinus orca) took fish from the longline at seven stations in the Bering Sea and three stations in the western Gulf of Alaska. These numbers are slightly higher than in previous years. Sperm whales (Physeter macrocephalus) were common near the vessel in the eastern gulf and the west Yakutat region and were observed taking fish from the line at several stations, similar to previous years.

Several special projects were conducted during the 2003 longline survey. Coral caught on the line were collected for identification and sample preservation; several specimens of exceptionally rare black coral (Antipatharia sp.) were collected. A seabird occurrence study was conducted for the second year -- the study is being conducted during several different surveys to address where and when certain seabird species occur in Alaska waters. In addition, the Alaska Department of Environmental Conservation is conducting a monitoring project for environmental contaminants in Alaskan fish. Fifty specimens of sablefish caught on the longline survey were collected throughout the Gulf of Alaska and the Bering Sea and sent to the department for contaminants analysis.

By Chris Lunsford.

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AFSC Quarterly
Research Reports
July-Sept 2003